conventions.java

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/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core;

import java.io.Externalizable;
import java.io.Serializable;
import java.lang.reflect.Proxy;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * Provides methods to support various naming and other conventions used
 * throughout the framework. Mainly for internal use within the framework.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 */
public abstract class Conventions {

	/**
	 * Suffix added to names when using arrays.
	 */
	private static final String PLURAL_SUFFIX = "List";


	/**
	 * Set of interfaces that are supposed to be ignored
	 * when searching for the 'primary' interface of a proxy.
	 */
	private static final Set ignoredInterfaces = new HashSet();

	static {
		ignoredInterfaces.add(Serializable.class);
		ignoredInterfaces.add(Externalizable.class);
		ignoredInterfaces.add(Cloneable.class);
		ignoredInterfaces.add(Comparable.class);
	}


	/**
	 * Determine the conventional variable name for the supplied
	 * code>Object</code> based on its concrete type. The convention
	 * used is to return the uncapitalized short name of the <code>Class</code>.
	 * So, <code>com.myapp.Product</code> becomes <code>product</code>.
	 * <p>For arrays, we use the pluralized version of the array component type.
	 * For <code>Collection</code>s we attempt to 'peek ahead' in the
	 * <code>Collection</code> to determine the component type and
	 * return the pluralized version of that component type.
	 */
	public static String getVariableName(Object value) {
		Assert.notNull(value, "Value must not be null");
		Class valueClass = null;
		boolean pluralize = false;

		if (value.getClass().isArray()) {
			valueClass = value.getClass().getComponentType();
			pluralize = true;
		}
		else if (value instanceof Collection) {
			Collection collection = (Collection) value;
			if (collection.isEmpty()) {
				throw new IllegalArgumentException("Cannot generate variable name for an empty Collection");
			}
			Object valueToCheck = peekAhead(collection);
			valueClass = getClassForValue(valueToCheck);
			pluralize = true;
		}
		else {
			valueClass = getClassForValue(value);
		}

		String name = StringUtils.uncapitalize(getShortName(valueClass));
		return (pluralize ? pluralize(name) : name);
	}

	/**
	 * Convert <code>String</code>s in attribute name format (lowercase, hyphens separating words)
	 * into property name format (camel-cased). For example, <code>transaction-manager</code> is
	 * converted into <code>transactionManager</code>.
	 */
	public static String attributeNameToPropertyName(String attributeName) {
		Assert.notNull(attributeName, "'attributeName' must not be null");
		if (attributeName.indexOf("-") == -1) {
			return attributeName;
		}
		char[] chars = attributeName.toCharArray();
		char[] result = new char[chars.length -1]; // not completely accurate but good guess
		int currPos = 0;
		boolean upperCaseNext = false;
		for (int i = 0; i < chars.length; i++) {
			char c = chars[i];
			if (c == '-') {
				upperCaseNext = true;
			}
			else if (upperCaseNext) {
				result[currPos++] = Character.toUpperCase(c);
				upperCaseNext = false;
			}
			else {
				result[currPos++] = c;
			}
		}
		return new String(result, 0, currPos);
	}

	/**
	 * Determine the class to use for naming a variable that contains
	 * the given value.
	 * <p>Will return the class of the given value, except when
	 * encountering a JDK proxy, in which case it will determine
	 * the 'primary' interface implemented by that proxy.
	 * @param value the value to check
	 * @return the class to use for naming a variable
	 */
	private static Class getClassForValue(Object value) {
		if (Proxy.isProxyClass(value.getClass())) {
			Class[] ifcs = value.getClass().getInterfaces();
			for (int i = 0; i < ifcs.length; i++) {
				Class ifc = ifcs[i];
				if (!ignoredInterfaces.contains(ifc)) {
					return ifc;
				}
			}
		}
		return value.getClass();
	}

	/**
	 * Determine the short name of the given class: without package qualification,
	 * and without the outer class name in case of an inner class.
	 * @param valueClass the class to determine a name for
	 * @return the short name
	 */
	private static String getShortName(Class valueClass) {
		String shortName = ClassUtils.getShortName(valueClass);
		int dotIndex = shortName.lastIndexOf('.');
		return (dotIndex != -1 ? shortName.substring(dotIndex + 1) : shortName);
	}

	/**
	 * Pluralize the given name.
	 */
	private static String pluralize(String name) {
		return name + PLURAL_SUFFIX;
	}

	/**
	 * Retrieve the <code>Class</code> of an element in the <code>Collection</code>.
	 * The exact element for which the <code>Class</code> is retreived will depend
	 * on the concrete <code>Collection</code> implementation.
	 */
	private static Object peekAhead(Collection collection) {
		Iterator it = collection.iterator();
		if (!it.hasNext()) {
			throw new IllegalStateException(
					"Unable to peek ahead in non-empty collection - no element found");
		}
		Object value = it.next();
		if (value == null) {
			throw new IllegalStateException(
					"Unable to peek ahead in non-empty collection - only null element found");
		}
		return value;
	}


	/**
	 * Return an attribute name qualified by the supplied enclosing {@link Class}. For example,
	 * the attribute name '<code>foo</code>' qualified by {@link Class} '<code>com.myapp.SomeClass</code>'
	 * would be '<code>com.myapp.SomeClass.foo</code>'
	 */
	public static String getQualifiedAttributeName(Class enclosingClass, String attributeName) {
		Assert.notNull(enclosingClass, "'enclosingClass' must not be null");
		Assert.notNull(attributeName, "'attributeName' must not be null");
		return enclosingClass.getName() + "." + attributeName;
	}

}